(1) Field of the Invention
The present invention relates to a control unit for actuating a pressure valve, in particular a pressure relief valve of an aircraft cabin. The control unit comprises an actuating body and a pressure-controlled actuator for operating the actuating body as a function of a predetermined threshold pressure value. The threshold pressure value is adjustable by an adjustment means.
(2) Description of Related Art
To protect an aircraft cabin against overloading due to excessive differential pressure between the cabin pressure and the ambient pressure independently of electronic regulating systems, usually a safety valve is used with a control unit in the form of a mechanical-pneumatic pressure switch. Such a conventional pressure switch comprises a sensor unit and a switching unit. The sensor unit includes a working spring, an adjustment spring and a power diaphragm. Depending on the rotation of an adjustment screw, the bias on the adjustment spring can be varied. However, the working range of the pressure switch is determined by the bias of the working spring. This working spring is fixed during assembly of the control unit, which fixes the bias and therefore the working range. The unit is assembled in such a way that the adjustment spring counteracts the working spring, wherein the switching point of the pressure switch results from the sum of the two counteracting spring biasing forces. To trigger the switching unit, a displacement is generated by means of the power diaphragm starting from a predetermined magnitude of the threshold pressure value, wherein a pressure force is applied to its active surface as a result of applying the differential pressure to it, wherein the displacement operates a valve tappet of the switching unit and thus brings a valve body, for example, into its open position.
In these well-known control units it has been found disadvantageous that the more stringent requirements with respect to the switching accuracy and the long-term behavior can no longer be fulfilled on the basis of the conventional design.